Electrically conductive organic material containing materials can be based on the mixture of polymer-containing matrix and conductive particles (fillers) embedded into this matrix. In the former case the matrix can also contain organic or inorganic additives and the electrically conductive particles either carbon, metal or metal oxide particles. The materials can also be directionally conductive.
In Sensors 2008 8 1595 (Maria Nordstrom & al. published 10 Mar. 2008 ISSN 1424-8220) it is illustrated how the conductivity of organic conductive layer on the substrate can vary with the deformations of the substrate. If the substrate deformations vary as a response to an external input, the conductivity variation can be used to sense this input, and the whole system forms a sensor. Ultimately, the layer can be located on a force microscope cantilever, particularly on an atomic force microscope (AFM) cantilever, whose tip is detecting a sample surface which acts as an external input for cantilever deformation.
In these cases, the conductive organic layer contains conductive particles or polymers that form a random network. When the substrate is bending in one direction, the conductive paths are loosened or broken in this direction but not perpendicular to it. Thus, the conductivity of the organic layer is not anisotropic in the first place, and the particle connections perpendicular to the deformation are essentially not influenced by deformation and are thus not contributing to the sensing phenomenon. There is a need for a sensor where the pathways are directed in this same direction, parallel to the deformation, thus being more sensitive to substrate bending.
A touch screen is an electronic visual display that can detect the presence and location of a touch within the display area using e.g. a finger, a hand or a stylus. Touch screens are used in many digital appliances, such as mobile phones, personal computers, electronic books, satellite navigation devices and video games.
A resistive touch screen panel is usually composed of layers using two thin, electrically conductive layers separated by a narrow gap. When an object, such as a finger, presses down on a point on the panel's outer surface, the two layers become connected at that point: the panel then behaves as a pair of voltage dividers with connected outputs. This causes a change in the electrical current, which is registered as a touch event and sent to a controller for processing. A resistive touch screen can also be piezoresistive; when pressed the conductivity of the material or wires increase and the controller detects where.
A capacitive touch screen panel consists of an insulator such as glass, coated with a transparent conductor such as indium tin oxide. As the human body is a conductor, touching the surface of the screen results in a distortion of the screen's electrostatic field, measurable as a change in capacitance. Different technologies known to someone skilled in the art may be used to determine the location of the touch. The location is then sent to a controller for processing. Examples of controllers are 3M Touch EX II 7000 Series for a capacitive screen or Semtech SX8650 for a resistive screen.
A touch screen can also combine capacitive and resistive sensing, e.g. detecting the proximity of one or more fingers, resulting in one action, and detecting one or more fingers tapping the screen resulting in another action. US20090189875A1 teaches one method for constructing a hybrid touch screen.
Problems with the current technologies for producing touchscreen panels are that transparent conductors such as indium tin oxide are expensive and have limited durability, and that resistive screens must be produced with several layers.
Nanomechanical cantilevers can be produced as micro fabricated silicon beams or using piezoelectric materials, as taught in U.S. Pat. No. 7,458,265. They are used as mechanical sensors, useful as mass and viscosity sensors, which transform processes occurring at their surface into a mechanical response. This signal transduction principle allows surface stress measuring at the cantilever surface by monitoring the bending of the cantilever and at the same time observing changes in the oscillation properties of the cantilever related to changes in mass load on the cantilever. Nanomechanical cantilevers can be used for chemical sensing such as detection of heavy metals, and as biosensors, e.g., for DNA and protein detection. Arrays of cantilever sensors can be employed for the parallel detection of multiple molecules of interest. Also, nanomechanical cantilever sensors can be used in surface and materials sciences for the real-time monitoring of self-assembled monolayer (SAM) formation, the detection of cholesterol interaction with hydrophobic surface layers and to study layer-by-layer build-up processes in real-time are possible, refer to Journal of Nanoscience and Nanotechnology, Volume 10, Number 4, April 2010 Koeser, Joachim & al: Nanomechanical Cantilever Sensors as a Novel Tool for Real-Time Monitoring and Characterization of Surface Layer Formation.
Touch sensors can be made by using Quantum Tunneling Composites (QTC) manufactured by Peratech Ltd. QTC is made from conductive filler particles, e.g. metal particles, combined with an elastomeric binder, typically silicone rubber, disclosed in WO/1999/038173. The metal particles are given an irregular structure with a spiked surface which is electrically insulated by the silicone rubber. The rubber allows the particles to get close but not touch even when the material is pressed or densely loaded. Increased charge on the spikes decrease the effective width of the potential barrier in quantum tunneling. This reduces the distance and energy required for the electron charge to tunnel through, and the material becomes conductive. The system with spiky particles is far more sensitive than the system with rounded particles would be. The conductance varies with the dynamic conditions. QTC are in general isotropic. There is a need for making anisotropic QTC in order to manufacture improved sensors.
“Multifunctional Chemical Vapor Sensors of Aligned Carbon Nanotube and Polymer Composites” by Wei & al. J. Am. Chem. Soc., 2006, 128 (5), pp 1412-1413, DOI: 10.1021/ja0570335 describes how partially coated perpendicularly aligned carbon nanotube arrays with an appropriate polymer thin film along their tube length can be used as sensors for chemical vapours, and also for mechanical deformations, thermal and optical exposures.
U.S. Pat. No. 7,777,478 discloses sensors based on nanotubes that can be used as touch and auditory sensors. In a similar way, US7673521 teaches how carbon nanotubes are grown from organometallic and incorporated into a polymer matrix to form a nanosensor which provides information regarding a physical condition of a material such as an airplane chassis or wing, in contact with the nanosensor.
There is a need for a better way to grow aligned conductive paths in a matrix, to form such sensors.
The object of the invention is to fulfil one or more or the above-mentioned needs, or to provide a useful alternative to existing methods and products.